Originally Posted by XQIZT
Volunteer Corvette has a spring with the same rate as the Moog you discuss above. Are you saying that would be too soft? We're getting ready to completely rebuild the front end as well, so what you are finding will be helpful.
If you are referring to the SU12H, that is listed for a NON AC BB. The picture shows 10 coils but there is no guarantee that the pic is actually of the spring in question.
The SU12H specifies "BB 4-SPD ALL; BB AUTO W/O AIR" and a 475 rate. This raises a red flag to me because GM did not have a "BB 4-SPD ALL" spring. The tags on mine are clearly 3931826, not 331318. This needs some clarification. Their SU12F looks like the Moog spring.
I am finding:
1) Many vendors are just reboxing the Moog spring and doubling or tripling the price. Fool me once, shame on you. Fool me twice, shame on me.
2) Many people are installing the Moog spring and say that the ride height is not affected even though the free length is several inches less. I believe this, but I don't believe the ride is the same as the OEM spring as this is a subjective matter.
3) GM created the 331318 specifically for NON AC BB cars. This apparently matches the Moog spring at some level. They developed the 3931826 spring for AC BB cars. They wouldn't have gone through that whole costly design and production process unless they had a reason.
Even though people attest that the Moog spring works fine, I am skeptical. I don't want to be the guinea pig here. I only want to do this once. I'm willing to pay a little more to get the right spring.
To complicate mattters, I am media blasting and painting all of the front end parts and the spring install tends to chew everything up requiring massive painstaking touch-ups. I also don't want to do that twice.
Several people have quoted a "325" number for the 3931826 but I don't know where that number comes from or what it means. The GM Parts catalog (group 7, p.7-1 C) has a build chart for 1972 19437 (coupe) which puts the spring at base 677.5lbs +A31/power windows 2.5lbs +C60/A/C 39lbs + J50/Power Brakes 4lbs +LS5/454 99.5lbs +N37/Tilt Wheel 1lb +N40/Power Steering 13lbs + U69/AM-FM Radio 3lbs + U79/Stereo Radio Amp 1lb for a total sprung weight (in my case) of 840.5 lbs. Don't know how this relates to the scheme of things but thought I should include it here.
It would seem likely that the 3931826 is somewhere between the Moog spring 474/ the 331318/475, and, the F41 550 spring.
FYI- The unbroken 3931826 spring on my 70 has exactly 10 coils and a free length of 15 inches at 95,000 miles.
I have a few more routes to try before I join the masses and use the Moog springs for $50. I can't justify paying the extra bucks for the incorrect
repro 331318 when the rate is nearly equivalent to the Moog. Waiting for responses to my inquiries.
Hope this helps rather than adds to the confusion.